1. Field of the Invention
The present invention relates to a method for producing polyester polyol, to an apparatus for producing polyester polyol by means of the producing method, to a polyester polyol produced by the producing method, and to a polyurethane foam obtained by use of the polyester polyol thus produced.
2. Description of the Background Art
It is known that polyester polyols in which an aromatic compound is introduced as a polyol component of the raw material of rigid polyurethane foam can be used to improve the flame retardance of the rigid polyurethane foam.
These polyester polyols can be obtained by reaction of e.g. short-chain glycol, such as ethylene glycol and diethylene glycol, and dibasic acid, such as phthalic acid. When terephtalic acid is used as the dibasic acid, the flame retardance of the rigid polyurethane foam can be improved to a large extent. Due to this, the polyester polyols in which the terephtalic acid is introduced are widely used as the polyol component of the raw material of the rigid polyurethane foam.
However, the polyester polyols using terephtalic acid as the raw material of the rigid polyurethane foam are significantly high in crystallinity, and as such may cause defects, such as reduction in mutual solubility with other components and reduction in workability, in the process of producing the rigid polyurethane foam.
Meanwhile, recovery polyethylene terephthalates, such as recovery PET bottles and recovery PET films, has been recycled increasingly in various fields in the recent years. In this connection, for example, Japanese Laid-open (Unexamined) Patent Publication No. Sho 60-130620 describes a process of producing polyester polyol, according to which reusable polyethylene terephthalate is allowed to react with diethylene glycol and at least one of the other oxyalkylene glycols and then sufficient ethylene glycol is stripped therefrom, to thereby produce the polyester polyol having the property of being not solidified or separated even when it is allowed to stand and thus being useful for the production of rigid polyurethane foam.
However, the process disclosed by the Japanese Laid-open (Unexamined) Patent Publication No. Sho 60-130620 has the following disadvantages. Although the sufficient ethylene glycol is stripped, since the stripped ethylene glycol is subjected to post-treatment as it is, efficient use of the raw material is not provided, and it is difficult to achieve extensive improvement of the production efficiency. Also, since the stripped ethylene glycol is subjected to post-treatment as it is, the process is complicated and the facility therefor is required. Further, although the polyester polyol obtained keeps its normal quality during the originally intended period from the production, some fine difference in prescription for preparation of the diethylene glycol and the at least one of the other oxyalkylene glycols used as the raw material could cause the polyester polyol to vary with age and consequently the polyester polyol may produce white turbidity, increase in viscosity or be crystallized.
It is an object of the present invention to provide a method for producing polyester polyol that can provide a simple process to produce extensively improved production efficiencies and also produce the polyester polyol of stable in quality. It is another object of the present invention to provide an apparatus for producing the polyester polyol produced by the method of the present invention. It is still another object of the present invention to provide the polyester polyol produced by the method of the present invention. It is a further object of the present invention to provide polyurethane foam obtained by use of the polyester polyol produced by the method of the present invention.
The present invention provides a novel method for producing polyester polyol by reaction of polyethylene terephthalate and raw polyol, wherein ethylene glycol which is a by-product of the reaction of polyethylene terephthalate and raw polyol is modified and the modified ethylene glycol is used as the raw polyol.
In this method, it is preferable that the ethylene glycol of the by-product is modified with alkylene oxide. Additionally, low-molecular-weight polyol may be used as the raw polyol, together with the modified ethylene glycol. It is preferable that a hydroxyl value of the raw polyol is in the range of 400-1,000 mgKOH/g.
Also, the present invention provides a novel apparatus for producing polyester polyol, which comprises a reaction vessel for allowing polyethylene terephthalate and raw polyol to react; a modifying vessel for modifying ethylene glycol distilled off from the reaction vessel; and a supply line for supplying the ethylene glycol modified in the modifying vessel to the reaction vessel as the raw polyol.
The present invention covers polyester polyol produced by reaction of polyethylene terephthalate and raw polyol, wherein the raw polyol comprises a modified ethylene glycol which is obtained by modifying ethylene glycol which is a by-product of the reaction of polyethylene terephthalate and raw polyol.
Further, the present invention covers polyurethane foam obtained by reaction of a polyol component comprising polyester polyol and a polyisocyanate component, wherein the polyester polyol is obtained by reaction of polyethylene terephthalate and raw polyol, and wherein the raw polyol comprises a modified ethylene glycol which is obtained by modifying ethylene glycol which is a by-product of the reaction of polyethylene terephthalate and raw polyol.
The method for producing polyester polyol of the present invention can provide the result of recycling the recovery polyethylene terephthalate effectively. Further, since the raw polyether is also reused from the distillate, wastes can be reduced by making good use of the raw polyol, thus providing an environmentally friendly result. Furthermore, the method of the present invention can provide the simple process requiring no post-treatment process of the distillate, so that the production efficiency can be improved to a large extent.
Thus, since the apparatus for producing polyester polyol of the present invention requires no facility for the post-treatment of the distillate, the apparatus is simple as a whole for the recycling facility. Besides, since there is provided the facility for modifying the distillate, efficient use of the raw polyol can be achieved.
With the polyester polyol of the present invention, quality variation with age is hardly caused and the good quality is always ensured.
As a result of this, the polyurethane foam of the present invention produced by use of the polyester polyol of the present invention can provide the fine cells, and can provide enhanced heat insulating efficiency.